Learning and kinematics of a particular type of throwing

Aims: The purpose of the present study was to analyze, on a sample of children between 9 and 10 years, the learning of a simple but not usual motor task, the launch of a tennis ball to hit a target, by varying the distribution of the practice and the arm (dominant or not dominant) used to execute the gesture. Materials and methods: The aim was to verify whether, after only 3 days of training, there is an improvement of gesture's efficiency (increased number of hit targets) related to specific change in the kinematics of the used arm. For this purpose we used a Wearable Inertial Sensors Device (WISD), capable of measuring movement-related data without any space limitation and with a no bulky set-up. Results: It has been observed that a training session of only 3 days was sufficient to achieve significant improvements in the success probability of a simple but not usual gesture, as the launch of a tennis ball to hit a target. The improvement was observed only when children used their dominant arm. Furthermore, the observed improvement is not associated to significant changes of some kinematic parameters of the gesture, as duration of performance, time to peak and peak acceleration. Conclusion: The probability of success of a gesture does not depend only on the kinematic characteristics of its final phase, the gesture itself, but also includes evidently a change of its 3D approach. Therefore, the effective change is not obtained by acting on the distal muscles of the upper limb, but mainly on the proximal ones, i.e. paravertebral and shoulder muscles, by involving the anticipatory postural adjustments, capable to compensate predictable perturbations before they occur.